1. Field of the Invention
This invention relates to gas-cooled windings of dynamoelectric machines, and more particularly, to means for electrically and mechanically connecting stator phase leads to split phase coils of such windings.
2. Description of the Prior Art
In large inner-cooled turbine generators which utilize a gas such as hydrogen as the cooling medium, the stator winding is usually split to facilitate heat transfer with an inner-cooling duct heat exchanging system. A split conductor arrangement is constructed by joining a large phase lead with two smaller winding conductors in an overlapping arrangement. The phase leads and winding conductors are composed of multiple conductor strands which are arranged in columns, and the combined cross-sectional area of the smaller conductor strands comprising the split winding is equal to the cross-sectional area of the larger conductor strands which comprise the phase lead. The smaller conductors, which are joined with the larger conductor in the end turn region of the stator, are extended in a parallel arrangement with the inner-cooling ducts through axial stator slots. The coolant is circulated through the cooling ducts in direct thermal contact with the current-carrying split winding conductors. The split conductor cooling arrangement has made it possible to greatly increase the maximum power capacities of large generators without exceeding the permissible limits of physical size.
In such heavy current conducting arrangements, high mechanical strength and good electrical conduction are required for the union of the phase lead and split winding conductors. Good electrical conduction and mechanical strength are interrelated fundamentally upon two factors: contact area and contact pressure. The effective contact area relative to the cross-sectonal area of the conductor is of great importance since it controls the resistance of the connection. It must remain uniform in size and not be affected by temperature changes or vibration. The contact pressure must be high enough so that adjacent conductor surfaces are pressed together with essentially all particles of the contact area being interlocked and free from insulating impurities. In a standard conductor group wherein a plurality of stranded conductors having a generally rectangular cross section are stacked one on top of another and two or more of such stranded groups are arranged in overlapping relation, adjacent strands within each group must be pressed together in a direction normal to the plane of the strand engagement, and similarly, adjacent groups must be pressed together in a direction which is normal to the plane of group engagement in order to achieve sufficient contact area and contact pressure. In general, the contact force should be great enough to produce a contact area which is equal to or greater than 1.5 times the cross-sectional area of the conductor. If the force holding the conductors together is too small, only the high points of the surface is touched and large currents passing through such a connection may develop heat and melt the metal at the high spots.
Proper contact pressure and contact area have been provided by a variety of prior art devices. Commonly used phase lead connectors include a one-piece "C" pressure clamp illustrated in FIG. 8 of the drawing. This connector clamp, formed of copper, is rolled to obtain the dimensions necessary to enclose the conductors. The rolled clamp provides only an approximate fit, however, and gaps remain after the pressure clamp is positioned around the stranded conductor union. Since these gaps must be closed during soldering to insure proper contact area and contact pressure, a large compressive force is applied to the connector as it is crimped around the overlapping conductors.
Considerable difficulty has been encountered in maintaining the required contact area and pressure throughout the expected life of the rolled "C" clamp connector. It has been observed that after the connectors are soldered and the compressive force is removed, the ends of the connector clamp tend to spring back to their original shape, resulting in residual tensile stresses in the soldered connection. Furthermore, unbonding of the soldered connection has been found to occur during operation of the turbine generator at high stator load currents. This unbonding is caused by various mechanical disturbances such as vibration and large magnetic forces which are induced by changes in high flux concentration surrounding these phase leads in the end turn regions. Also, when the soldered connection is subjected to high temperatures which accompany heavy current flow, the contact pressure at the union of the conductors is relaxed.
A second type of connector, which avoids some of the disadvantages of the "C" clamp connector, is a two-piece bolted connector which compresses the overlapping conductor groups uniformly in a single direction. Such a connector has been described in the pending application of F. Fidei, Ser. No. 533,406, filed Dec. 16, 1974. This two-piece interlocking connector eliminates the damaged strand problem since the strands are not twisted or otherwise deformed as the connector is tightened about the overlapping stranded conductor groups. However, it applies controllable compression in only one direction and thus does not constrain all variables which determine the quality of the connection. In addition, since bolts must be inserted from both sides of the connector, an assembly problem arises in that the two-piece bolted connectors are generally located side-by-side in pairs, and the bolt heads in the gap between the connectors interfere with the clearance required for induction soldering and ultrasonic testing.
These problems stem directly from the lack of precision in the fitting of the prior art connectors about the conductor strands and in the lack of means for applying and maintaining uniform pressure upon the overlapping conductor groups and adjacent conductors within each group. It is, therefore, a principal object for the present invention to provide a connector having a conductor receiving region which may be accurately adjusted to provide a closely conforming fit for an overlapping, stranded conductor assembly and which also includes means for maintaining controlled, uniform contact pressure of sufficient magnitude and in the proper directions to insure good electrical conductivity as well as mechanical strength.